1. Field of the Invention
This invention pertains generally to devices for detecting radiation, and more particularly to devices for detecting neutrons and gross gamma radiation.
2. Description of Related Art
Neutron and gamma radiation detectors are important devices for providing large area radiation monitoring, such as in the homeland defense initiative. These detectors can be used, for example, as linear sensor arrays along highways or railways, as rings of detectors surrounding critical nuclear, military, or government facilities, or as individual networked detectors for cargo ships, harbor cranes, or luggage screening systems. In addition to the area of homeland security, neutron and gamma detectors can also be used in the “traditional” neutron applications of nuclear safeguards and waste measurements.
Various types and configurations of neutron and gamma detectors have been previously developed. For example, detectors, or proportional counters, lined with helium-3 (3He), boron triflouride (BF3) and boron-10 (10B) are a very mature and stable technology. However, they can be extremely expensive due to complex manufacturing processes and high material costs. Similarly, 6Li glass fiber or 10B doped scintillation detectors are also extremely expensive, and moreover, they can exhibit significant temperature and high voltage dependencies. Furthermore, these detectors typically rely on complicated gamma/neutron separation techniques. In general, scintillator based neutron detectors are unable to achieve high levels of geometric efficiency at moderate cost levels.
Classical 3He proportional counters rely on gas multiplication gain to perform detection. These detectors are generally configured in a cylindrical geometry that in some cases may utilize the moderating material as the structural support to reduce overall weight. It should be recognized that the use of proportional counters, because of the inherent gas multiplication process, require orders of magnitude higher gas purity than ionization chambers. However, the working gas in such units is permanently sealed within the detection volume and subject to the build-up of impurities. A thin sense wire within the detection device passes through the cylinder and functions as a collecting electrode. The collecting electrode is connected to a high voltage bias source requiring that the connected sense components be able to resist these high voltages, while the high voltage is disadvantageously exposed to the surrounding environment. Signals at the collecting electrode are also directly subject to noise from the high voltage power supply. Furthermore, the collecting electrode is difficult to mount, induces additional detector capacitance and is susceptible to acoustic noise and vibration, wherein the proportional counter must rely on significant gas multiplication effects to provide sufficient signal-to-noise margins.
Therefore, there is a need for an apparatus for the detection of neutrons and gross gamma radiation that recognizes the present drawbacks and provides a solution to one or more of the problems associated therewith. The present invention satisfies that need, as well as others, and overcomes deficiencies in previously developed detection devices.